Do the impossible with cats, proverbially (4)
I believe the answer is:
herd
'do the impossible with cats proverbially' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for herd that I've seen before include "Animal group" , "People in the mass" , "Bunch of cattle" , "Assemblage" , "cattle together" .)